Embryo Transfer

Abstract

In order to gain knowledge and to maximize the efficiency of embryo transfer to the uterine cavity following in vitro fertilization, it is important to appreciate the complexities of the natural process. Our knowledge of tubal factors contributing to oocyte entry into the tube, fertilization, nourishment of the embryo and the control mechanisms operating to synchronize embryo transport into the uterine cavity at a time when it is capable of further development and eventual successful implantation is incomplete, particularly in the human (Pauerstein and Eddy 1979). Transport of ova in women is characterized by retention in the ampulla for approximately 72 h followed by rapid transit through the isthmus, and the time from ovulation to arrival in the endometrial cavity is about 80 h (Croxatto and Ortiz 1975). Less is known of the mechanisms regulating ovum or zygote transport. It has been demonstrated that the ovum’s or embryo’s inability to pass the ampullary-isthmic junction coincides with the presence of oestrogen-dependent tenacious mucus in the isthmic lumen during the ovulatory and immediate postovulatory period, which may aid sperm transport against the normal cilia beat which is not well developed at this stage of the cycle (Jansen 1980). It is hypothesized that 2 to 3 days after ovulation, when progesterone levels are high, the mucus disappears coincident with the appearance of isthmic cilia, which beat towards the uterus, and relaxation of the isthmic musculator, thus allowing oocyte or embryo transport to the uterus. In non-human primates, premature entry of the embryo into the uterus significantly reduces implantation rates (Adams 1980).